Recomp: Building Muscle + Losing Fat Works W/ Weights, but Won't Boost 'Ur Resting Metabolic Rate Along the Way

There are even equations which indicate that any increase in lean mass should contribute to measurable increases in your resting metabolic rate aka your "RMR". Being able to build muscle and thus increase your metabolic rate is one of the reasons why everyone (including myself) recommends to hit the weights (not just the cardio apparel) whenever you're trying to shed superfluous body fat.

Now, a recent study from the University of Ottawa clearly suggests that, "despite an increase in fat-free mass [...] 6 months of aerobic, resistance, or combined training [adherence was controlled for] did not increase RMR compared [...] in adolescents with obesity" (Alberga. 2017).

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In view of the energy thirst of your muscle and organ mass (total lean mass) this result seems odd. Needless to say that it is thus worth taking a look at the studies goals and methodology. As far as the first is concerned, the articles write that they started with the (logical) hypothesis that "resistance exercise training performed alone or in combination with aerobic exercise training would increase [the] resting metabolic rate (RMR) relative to aerobic-only and nonexercising control"(Alberga. 2017) groups.

In their subjects, postpubertal adolescents (N = 304) aged 14–18 years with obesity (body mass index (BMI) ≥ 95th percentile) or overweight (BMI ≥ 85th percentile + additional diabetes risk factor(s)), who were randomized to 4 groups for 22 weeks however, the scientists did not observe the expected increase in RMR in response to the four weekly sessions of ...

Aerobic exercise training - Participants exercised on treadmills, cycle ergometers, and/or elliptical machines at an intensity of 65%–85% of their previously measured HRmax for 20–45 min per session, gradually progressing in intensity and duration until the end of the intervention

Resistance exercise training - Participants performed up to 3 sets of 7 exercises on resistance machines for 6–15 repetitions of their maximum for 20–45 min per session (supplementary Tables S3, S41). Participants were recommended to rest for 1.5 to 2 min between sets. Intensity of resistance training gradually increased by increasing the load (weight) that adolescents were lifting for a fewer number of repetitions, targeting progressive improvements in muscular strength

Combined aerobic and resistance exercise training - Participants performed both the Aerobic and the Resistance exercise training components during each exercise session

Working out was yet only one pillar of the subjects' weight/fat loss I plotted in Figure 1. The other pillar was a diet containing 250kcal less than the subjects maintenance diet.

What is surprising, however, is that the intended increases in lean mass did not translate into increased rates of metabolic rate (note: non-adherence cannot explain the difference, the scientists' per-protocol analyses including only participants with ≥70% adherence to our prescribed 4 sessions/week showed the same trends such that there were no between-group differences in fat-free mass and RMR following the 6-month exercise trial).

Do not jump to false black-and-white conclusions: I know, life would be easier if there were just black and white, but it would also be boring without "color" or, as in the case of the effects of lean mass on one's resting energy expenditure, the nuances of relevant vs. irrelevant lean mass gains. There's no doubt about it: Lean mass gains or losses of 10% of the total body weight will have significant beneficial/negative effects on your RMR (the overall effect will yet also depend on fat loss). If you scrutinize the data from the study at hand, the meager 900g of muscle and 1.8 kg of total lean mass the resistance training group added to their overweight frames amounts to only 1-2% of the subjects' total body mass. And still, the scientists are right, when they say that there's a "widespread misperception that resistance training increases RMR through its direct effect on increasing fat-free mass" (Alberga. 2017). It is, and this takes us back to where we have been coming from, more complex than that... but that's a topic for another SuppVersity article and another study with different subjects and greater increases in lean and decreases in fat mass.

As the data from the meta-analysis by Schwartz et al. (Figure 3) shows, that is not really surprising. It is well established that weight loss - albeit in this case in adults and of (in almost all cases) significantly more body mass - will almost linearly reduce subjects' metabolic rate.

Figure 3: Comparison of the mean rate of changes in resting energy expenditure relative to weight loss with different weight-loss interventions in all men and women (n = 2983). * and † indicate significant difference from the diet at P < 0.05 and P < 0.001 respectively (Schwartz. 2010).

Against that background, it is, even though the study at hand proves that the lean mass loss is not primarily responsible for the problem of reduced RMRs, important to point out that the resistance training group lost the most body fat (calculated as difference between total lean mass and total body weight), namely 1.8kg and thus twice as much as the aerobic training group (-1.8kg) and almost thrice as much as the control group (-0.5). This and previous evidence showing that resistance training can ameliorate the reduction in RMR, as well, do thus clearly speak in favor of hitting the weights when trying to shed body fat (or as it happened in this case: "recomp").

What do other studies show: Well, compared to Lazzer et al. who observed decreases in RMR with weight loss in youths on a combined diet (-15-20%) and exercise (2x per week physical education, 2x p. week combined training) intervention, the study at hand is good news for teens trying to shed body fat. With a duration of 9 months and a higher caloric deficit and thus weight loss (-16-18kg), the reason for the RMR reduction in this previous study could indeed be what people often label metabolic damage. Now, what is interesting, is that this "damage" can, once again, not be explained by lean mass losses, because only the girls lost lean mass, while both groups in Lazzer et al. showed sign. reductions in RMR. Similar decreases were observed in other pertinent studies (Foschini. 2010; Inoue. 2015), as well as studies in adults (Bray. 1969; Cameron. 2008, 2010; Doucet. 2000, 2001, 2003; Schwartz. 2010), studies that do yet also indicate that working out while dieting can mitigate this effect.

So is the "do resistance training to build lean mass and lose body fat"-advice bogus? Well, I'd say the study at hand shows that the effect of small increases in lean mass as they were observed in the study at hand have marginal effects on overweight / obese young subjects (that could be different in older subjects, but I honestly doubt that a maximal muscle gain of 0.9kg (in the RT group) would make a measurable, sign. difference in adults and/or people of whom nobody would claim that they were metabolically damaged due to overweight (note: the study does not provide evidence in favor of the theory of metabolic damage).

As the authors point out in their conclusion, their study does yet only confirm that the idea that "resistance training increases RMR through its direct effect on increasing fat-free mass" is a "widespread misperception" - at least if you understand that to be a linear effect that begins with the first lbs of muscle you add to your frame. This does not mean that working out in general and resistance training, in particular, were useless. After all, the real takeaway messages of the study are not just (a) that even a very small caloric deficit (for someone who drinks soft drinks or sweetened coffee, it would often suffice to drop those) can have a significant weight/fat loss effect in the longer run (here 6 months), but also that (b) this effect will be most pronounced (keep in mind that the difference did not reach statistical sign. in the 6 months study period, though) in conjunction with resistance training - in this case even more pronounced than with combined training (1.8kg fat loss vs. 1.2kg fat loss), for which data from Byrne et al. (2001) suggests that its reduced ability to build muscle could be the culprit | Comment on Facebook!

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